WPAN [Wireless Personal Area Network] networks are known since some years; a PAN [Personal Area Network] network can be defined as a computer network for communicating among devices close to one person; a WPAN network is a PAN network using wireless short-range communication technologies.
A communication technology which is very often used for implementing a WPAN network is ZigBee.
One of the main and recent applications of WPAN networks is WSN [Wireless Sensor Network] networks.
In a WPAN the key components are the nodes of the network, also called devices; basically, there are two types of devices: FFD [Full Function Device] and RFD [Reduced Function Device]; usually, a WPAN network requires that at least one FFD device acts as a WPAN coordinator; FFD devices have the task to communicate with RFD devices and to route communication across the network; often FFD devices are mains powered while RFD are battery powered.
Depending on the application, a WPAN network may operate in different topologies: the star topology, the cluster tree topology and the mesh topology; WSN networks typically use the mesh topology; the present invention is particularly useful in this case.
In a traditional ZigBee network, there are three types of nodes, namely a ZigBee end device (which is often a RFD device) and a ZigBee coordinator (which is a FFD device) and a ZigBee router (which is a FFD device).
In a traditional WSN network based on the ZigBee technology, the end devices (also called “edge nodes”) are battery powered and therefore are designed to limit power consumption while the routers and the coordinator (which is also a router) are mains supplied and therefore do not have problems with power consumption.
The component of a node of a WPAN network which is primarily responsible for power consumption is the radio transceiver; therefore, the typical way of reducing power consumption is to use “duty-cycling”, i.e. to let the radio transceiver of the end devices operate intermittently for short period of times; of course, this complicates the communication protocols used in WPAN networks.
From the prior art, there are also known WSN networks wherein all the nodes are battery powered and therefore are designed to limit power consumption and wherein special MAC protocols are used to limit power consumption of the radio transceivers. For example, the article by M. Buetter et al, “X-MAC: A Short Preamble MAC Protocol for Duty-Cycled Wireless Sensor Networks”, SenSys 2006, 1-3 Nov. 2006, Boulder, Colo., USA, describes in detail one of such MAC protocols called “X-MAC” and refers to others of such MAC protocols, namely “S-MAC”, “T-MAC”, “B-MAC” and “WiseMAC”.
The problem of power consumption in wireless networks has already been considered in the past and solved through specific solutions.
From U.S. Pat. No. 7,035,240 there is known a method and network architecture for implementing an energy efficient network. The network includes a plurality of nodes that collect and transmit data that are ultimately routed to a base station. The network nodes form a set of clusters with a single node acting as a cluster-head. The cluster-head advertises for nodes to join its cluster, schedules the collection of data within a cluster, and then transmits the data to the base station. A cluster can intelligently combine data from individual nodes. After a period of operation, the clusters are reformed with a different set of nodes acting as cluster-heads. The network provides an increased system lifetime by balancing the energy use of individual nodes.
From U.S. Pat. No. 7,020,501 there is known a system for conserving energy in a multi-node network, in particular a sensor network; the network includes nodes configured to organize themselves into tiers; the nodes are further configured to produce a transmit/receive schedule at a first tier in the network and control the powering-on and powering-off of transmitters and receivers in nodes in a tier adjacent to the first tier according to the transmit/receive schedule. A number of monitor points connected to an external network are provided in communication with the sensor network.
Interoperability between different communication standards or between different releases of the same standard is in general a well known big issue and in the past it has been addressed and solved in many different ways depending on the particular case. The issue of compatibility may be at any of the different levels of the ISO/OSI stack.
A typical approach to the above problem is to provide one or more components of the network that support(s) both standards or both releases and to carry out a “translation”. To this regard, the following US patents and US patent applications may be quoted: U.S. Pat. No. 6,657,984, 2003139151, 2005180453, 20060056448.